Spears, 26, called in sick to a court-ordered deposition Dec. 12, although she was photographed that day driving with a friend.

"She was, in fact, out later that day and night," Kaplan said. "It's not fourth grade where you get a doctor's note and it's all OK."

Spears and Federline have been wrangling for months over custody of their sons, 2-year-old Sean Preston and 1-year-old Jayden James.

Federline, 29, has temporary custody of the children because Spears, who has limited visitation rights, has defied court orders. Spears and Federline were married in October 2004 and finalized their divorce in July.